1. Field of the Invention
This invention relates to a wire dot printer head and a wire dot printer.
2. Discussion of the Background
A wire dot printer head is an apparatus which performs printing by rocking, between a waiting position and a printing position, an armature with a printing wire connected thereto, to strike the front end of the wire on a printing medium such as a sheet when the armature is rocked to the printing position.
As the wire dot printer head, there has been developed an apparatus for printing by the use of a magnetic circuit which attracts an armature from a waiting position to a printing position with a magnetic flux formed by a coil around the armature to be rocked. As shown in FIGS. 14 and 15, in such a wire dot printer head 100, an armature 102 supporting a printing wire 101 has a support shaft 103. The armature 102 is supported rotatably on the center of the support shaft 103. An armature spacer 105 has a cutout section 104 in which the support shaft 103 of the armature 102 is fitted, and is mounted on a yoke 106 for the formation of the magnetic circuit. On the armature spacer 105, a plate 108 is provided to hold the support shaft 103 which restricts the movement of the armature 102 through an elastic spacer 107 elastically fixing the position of the support shaft 103 of the armature 102. It is possible to thereby prevent abrasion of the plate 108 likely to be caused by the support shaft 103 of the armature 102, and accordingly to fix the position of the support shaft 103.
With recent speedups of printing operation, however, the armature 102 is likely to violently vibrate during printing because of such a high-speed movement between the printing position and the waiting position as 2500 times per second. The support shaft 103, on the center of which the armature 102 rotates, therefore, tends to abrade the surface of the yoke 106. It is generally because the yoke 106 is formed of a softer magnetic material than the support shaft 103 of the armature 102. If the surface abrasion of the yoke 106 proceeds, the support shaft 103 of the armature 102 will move off position, resulting in unstable rocking operation of the armature 102 and accordingly in a deteriorated printing quality.
Furthermore, the support shaft 103 of the armature 102 is moved not only in the rocking direction of the armature 102 but in the radial direction of the armature spacer 105 by vibrations caused by the speedups of the printing operation, resulting in unstable rocking operation of the armature 102. Furthermore, if the surface abrasion of the yoke 106 caused by the support shaft 103 of the armature 102 proceeds, the armature 102 for instance will contact the coil flange and the support shaft 103 will make fine vibrations to rub off stock of the cutout section 104 of the armature spacer 105. Consequently, a shortened life of the wire dot printer head 100 will result.
It is, therefore, an object of this invention to provide wire dot printer head and wire dot printer which are capable of restraining the abrasion of the yoke surface in order to prevent the deterioration of printing quality.
The object of this invention can be accomplished by novel wire dot printer head and wire dot printer of this invention.
Therefore, according to the novel wire dot printer head and wire dot printer of this invention, there are provided, on a yoke for holding a plurality of armature support shafts, an abrasion preventive member which encloses the outer periphery of the armature support shafts, together with an armature spacer having a plurality of cutout sections in which the armature support shafts for supporting a printing wire are inserted. Thus it is possible to prevent the direct contact of the armature support shafts with the yoke.